Acoustic resonator devices and methods providing patterned functionalization areas

ABSTRACT

A micro-electrical-mechanical system (MEMS) resonator device includes a top side electrode overlaid with an interface layer including a material having a surface (e.g., gold or other noble metal, or a hydroxylated oxide) that may be functionalized with a functionalization (e.g., specific binding or non-specific binding) material. The interface layer and/or an overlying blocking material layer are precisely patterned to control locations of the interface layer available to receive a self-assembled monolayer (SAM), thereby addressing issues of misalignment and oversizing of a functionalization zone that would arise by relying solely on microarray spotting. Atomic layer deposition may be used for deposition of the interface layer and/or an optional hermeticity layer. Sensors and microfluidic devices incorporating MEMS resonator devices are also provided.

STATEMENT OF RELATED APPLICATIONS

This application is a non-provisional of U.S. Provisional PatentApplication No. 62/246,302 filed on Oct. 26, 2015, the disclosure ofwhich is hereby incorporated by reference herein in its entirety.Subject matter disclosed herein also relates to the following three U.S.patent applications each filed or to be filed on Oct. 26, 2016: (1) U.S.patent application Ser. No. 15/334,528, entitled “Acoustic ResonatorDevices and Fabrication Methods Providing Hermeticity and SurfaceFunctionalization;” (2) U.S. patent application Ser. No. 15/334,482,entitled “Acoustic Resonator Devices and Methods with Noble Metal Layerfor Functionalization;” and (3) U.S. patent application Ser. No.15/334,459, entitled “Acoustic Resonator Device with ControlledPlacement of Functionalization Material;” wherein the contents of theforegoing three U.S. patent applications are hereby incorporated byreference as if set forth fully herein.

TECHNICAL FIELD

The present disclosure relates to acoustic resonator devices, includingacoustic wave sensors and microfluidic devices suitable for biosensingor biochemical sensing applications.

BACKGROUND

A biosensor (or biological sensor) is an analytical device including abiological element and a transducer that converts a biological responseinto an electrical signal. Certain biosensors involve a selectivebiochemical reaction between a specific binding material (e.g., anantibody, a receptor, a ligand, etc.) and a target species (e.g.,molecule, protein, DNA, virus, bacteria, etc.), and the product of thishighly specific reaction is converted into a measurable quantity by atransducer. Other sensors may utilize a non-specific binding materialcapable of binding multiple types or classes of molecules or othermoieties that may be present in a sample, such as may be useful inchemical sensing applications. The term “functionalization material” maybe used herein to generally relate to both specific and non-specificbinding materials. Transduction methods may be based on variousprinciples, such as electrochemical, optical, electrical, acoustic, andso on. Among these, acoustic transduction offers a number of potentialadvantages, such as being real time, label-free, and low cost, as wellas exhibiting high sensitivity.

An acoustic wave device employs an acoustic wave that propagates throughor on the surface of a piezoelectric material, whereby any changes tothe characteristics of the propagation path affect the velocity and/oramplitude of the wave. Presence of functionalization material embodiedin a specific binding material along an active region of an acousticwave device permits a specific analyte to be bound to the specificbinding material, thereby altering the mass being vibrated by theacoustic wave and altering the wave propagation characteristics (e.g.,velocity, thereby altering resonance frequency). Changes in velocity canbe monitored by measuring the frequency, magnitude, or phasecharacteristics of the sensor, and can be correlated to a physicalquantity being measured.

In the case of a piezoelectric crystal resonator, an acoustic wave mayembody either a bulk acoustic wave (BAW) propagating through theinterior of a substrate, or a surface acoustic wave (SAW) propagating onthe surface of the substrate. SAW devices involve transduction ofacoustic waves (commonly including two-dimensional Rayleigh waves)utilizing interdigital transducers along the surface of a piezoelectricmaterial, with the waves being confined to a penetration depth of aboutone wavelength. In a BAW device, three wave modes can propagate, namely,one longitudinal mode (embodying longitudinal waves, also calledcompressional/extensional waves), and two shear modes (embodying shearwaves, also called transverse waves), with longitudinal and shear modesrespectively identifying vibrations where particle motion is parallel toor perpendicular to the direction of wave propagation. The longitudinalmode is characterized by compression and elongation in the direction ofthe propagation, whereas the shear modes consist of motion perpendicularto the direction of propagation with no local change of volume.Longitudinal and shear modes propagate at different velocities. Inpractice, these modes are not necessarily pure modes as the particlevibration, or polarization, is neither purely parallel nor purelyperpendicular to the propagation direction. The propagationcharacteristics of the respective modes depend on the materialproperties and propagation direction respective to the crystal axisorientations. The ability to create shear displacements is beneficialfor operation of acoustic wave devices with fluids (e.g., liquids)because shear waves do not impart significant energy into fluids.

Certain piezoelectric thin films are capable of exciting bothlongitudinal and shear mode resonance, such as hexagonal crystalstructure piezoelectric materials including (but not limited to)aluminum nitride (AlN) and zinc oxide (ZnO). To excite a wave includinga shear mode using a piezoelectric material layer arranged betweenelectrodes, a polarization axis in a piezoelectric thin film mustgenerally be non-perpendicular to (e.g., tilted relative to) the filmplane. In biological sensing applications involving liquid media, theshear component of the resonator is used. In such applications,piezoelectric material may be grown with a c-axis orientationdistribution that is non-perpendicular relative to a face of anunderlying substrate to enable a BAW resonator structure to exhibit adominant shear response upon application of an alternating currentsignal across electrodes thereof.

Typically, BAW devices are fabricated by micro-electro-mechanicalsystems (MEMS) fabrication techniques owing to the need to providemicroscale features suitable for facilitating high frequency operation.In the context of biosensors, functionalization materials (e.g.,specific binding materials; also known as bioactive probes or agents)may be deposited on sensor surfaces by microarray spotting (also knownas microarray printing) using a microarray spotting needle.Functionalization materials providing non-specific binding utility(e.g., permitting binding of multiple types or species of molecules) mayalso be used in certain contexts, such as chemical sensing.Unfortunately, dimensional tolerances for microarray spotting are largerthan dimensional tolerances enabled by MEMS fabrication techniques. Anexcess of specific binding material may reduce sensor response, such asby impairing a lower limit of detection. Separately, an excess ofexposed non-specific binding material may lead to undesirable attachmentof analyte when a device is in use. Although localized chemical orbiological blocking techniques (e.g., using blocking buffers orproteins, such as bovine serum albumin (BSA), polyethylene oxide (PEO),or ethanolamine) could potentially be used to prevent or reducenon-specific binding, such blocking may require cumbersome empiricaltesting and may complicate device manufacturing. Moreover, the abilityto stably operate BAW resonators in the presence of liquid may belimited, particularly for BAW resonators utilizing electrodes composedof reactive metals (e.g., aluminum or aluminum alloy) that aresusceptible to corrosion when contacted with liquid. Hypotheticalapplication of material over such electrodes must be carefullyconsidered to avoid excess thickness that could dampen acousticvibration and result in degraded performance. Surface compatibility offunctionalization (e.g., specific binding) materials in the vicinity ofsuch electrodes is also a concern, as is cost-effective and repeatablemanufacturing.

Accordingly, there is a need for acoustic resonator devices suitable foroperation in the presence of liquid for biosensing or biochemicalsensing applications without negatively impacting device performance.

SUMMARY

The present disclosure provides a micro-electrical-mechanical system(MEMS) resonator device arranged on a substrate, the MEMS resonatordevice including a piezoelectric material layer, an interface layer, anda self-assembled monolayer (SAM) suitable for functionalization (e.g.,by receiving at least one functionalization material) arranged over atleast a portion of an active region of the device, wherein less than anentirety of the piezoelectric material layer is overlaid with interfacelayer material that is available to receive a SAM. In certainembodiments, the interface layer is arranged over less than an entiretyof the piezoelectric material layer, or a patterned blocking layer(e.g., at least one of silicon nitride [Si₃N₄], silicon carbide [SiC],photoresist (e.g., including but not limited to SU-8), polyimide,parylene, or poly (ethylene glycol) [PEG]) is arranged over at least aportion of the interface layer, whereby presence of the patternedblocking material renders a portion of the interface layer unavailableto receive a SAM.

Deposition techniques such as atomic layer deposition (ALD), chemicalvapor deposition (CVD), or physical vapor deposition (PVD) may be usedin conjunction with one or more masks (e.g., photolithographic masks) topattern the interface layer over at least certain portions of a MEMSresonator device (e.g., less than an entirety of a MEMS resonator devicein certain embodiments), including at least a portion of an activeregion. The interface layer may comprise a material including ahydroxylated oxide surface, or gold or another noble metal, suitable forattachment of an organosilane-based SAM. An interface layer comprising ahydroxylated oxide surface may receive a SAM comprising an organosilanematerial, or an interface layer comprising gold or another noble metalmay receive a SAM comprising a thiol material. By pre-defining apatterned interface layer with a high dimensional tolerance, forming aSAM registered with the interface layer, and then applying afunctionalization (e.g., specific binding or non-specific binding)material to the SAM, a higher dimensional tolerance may be achieved forpositioning of the functionalization material than could be attained bymicroarray spotting alone. In this manner, misalignment and overprintingchallenges of microarray spotting can be overcome by improved patterningof underlying layers (i.e., an interface layer and SAM) that may be usedto dictate placement of functionalization material. In certainembodiments incorporating electrode materials subject to corrosion, ahermeticity layer may also be applied between a top side electrode andthe interface layer, with the hermeticity layer serving to protect thetop side electrode. Microfluidic devices incorporating MEMS resonatordevices disclosed herein are further provided, as well as methods forforming MEMS resonator devices and microfluidic devices.

In one aspect, a micro-electrical-mechanical system (MEMS) resonatordevice includes a substrate; a bulk acoustic wave resonator structurearranged over at least a portion of the substrate, an interface layer,and a self-assembled monolayer (SAM). The bulk acoustic wave resonatorstructure includes a piezoelectric material, a top side electrodearranged over a portion of the piezoelectric material, and a bottom sideelectrode arranged between the piezoelectric material and the substrate,wherein a portion of the piezoelectric material is between the top sideelectrode and the bottom side electrode to form an active region. Theinterface layer is arranged over at least a portion of the activeregion, wherein less than an entirety of the piezoelectric material isoverlaid with interface layer material that is available to receive aself-assembled monolayer (SAM). The SAM is arranged over at least aportion of the interface layer. In certain embodiments, the interfacelayer comprises a hydroxylated oxide surface, and the self-assembledmonolayer comprises an organosilane material. In certain embodiments,the interface layer comprises gold or another noble metal, and theself-assembled monolayer comprises a thiol material.

In certain embodiments, the interface layer is arranged over less thanan entirety of the piezoelectric material. In certain embodiments, apatterned blocking layer is arranged over at least one portion of theinterface layer. Such a blocking layer preferably comprises a materialto which a self-assembled monolayer (SAM) is substantially non-adherent.In certain embodiments, such a patterned blocking layer may comprise atleast one of Si₃N₄, SiC, photoresist (e.g., SU-8), polyimide, parylene,or poly(ethylene glycol). In certain embodiments, patterns may bedefined in a blocking layer via etching. In the case of a patternedblocking layer comprising silicon nitride [Si₃N₄], an underlyinginterface (e.g., SiO₂) layer is preferably engineered to take intoaccount the relative etch rates of the blocking layer material (e.g.,Si₃N₄) and the interface layer material (e.g., SiO₂) in a dry etchprocess such as reactive ion etch with sulfur hexafluoride [SF₆].Presence of a patterned blocking layer eliminates the need forbiological or chemical blocking of the SAM to prevent binding offunctionalization material in undesired locations. In certainembodiments, at least one functionalization (e.g. specific binding ornon-specific binding) material is arranged over at least a portion ofthe self-assembled monolayer, wherein at least a portion of the at leastone functionalization material is registered with the active region. Incertain embodiments, the interface layer comprises at least one ofsilicon dioxide [SiO₂], titanium dioxide [TiO₂], tantalum pentoxide[Ta₂O₅], hafnium oxide [HfO₂], or aluminum oxide [Al₂O₃]. In certainembodiments, the top side electrode comprises a non-noble metal, and theMEMS resonator device further comprises a hermeticity layer arrangedbetween the interface layer and the top side electrode. In certainembodiments, the hermeticity layer comprises an oxide, a nitride, or anoxynitride dielectric material, and the hermeticity layer comprises awater vapor transmission rate of no greater than 0.1 (g/m²/day). Incertain embodiments, the hermeticity layer comprises a thickness in arange of from about 5 nm to about 100 nm, from about 5 nm to about 50nm, or from about 10 nm to about 25 nm, and the interface layercomprises a thickness in a range of from about 1 nm to about 50 nm, orfrom about 2 nm to about 20 nm, or from about 5 nm to about 15 nm. Incertain embodiments, a blocking layer is patterned over a portion of atleast one of the top side electrode or the piezoelectric material,wherein the blocking layer is non-overlapping with respect to the activeregion. In certain embodiments, the piezoelectric material comprises ahexagonal crystal structure piezoelectric material (e.g., aluminumnitride or zinc oxide) that comprises a c-axis having an orientationdistribution that is predominantly non-parallel to (and may also benon-perpendicular to) normal of a face of the substrate. In certainembodiments, an acoustic reflector structure is arranged between thesubstrate and the bulk acoustic wave resonator structure, wherein thebulk acoustic wave resonator structure comprises a solidly mounted bulkacoustic wave resonator structure. In other embodiments, the substratedefines a recess, and the MEMS resonator device further comprises asupport layer arranged between the bulk acoustic wave resonatorstructure and the recess, wherein the active region is arranged over atleast a portion of the support layer and at least a portion of therecess, such as to form a film bulk acoustic wave resonator (FBAR)structure.

In certain embodiments, the self-assembled monolayer comprises anorganosilane material. In certain embodiments, the top side electrodecomprises a noble metal not overlaid with a hermeticity layer.

Certain embodiments are directed to a sensor comprising a MEMS resonatordevice as disclosed herein, and/or to a fluidic (e.g., microfluidic)device incorporating a MEMS resonator device as disclosed herein with afluidic passage arranged to conduct a liquid to contact the at least onefunctionalization material.

In another aspect, a method for biological or chemical sensing includessupplying a fluid containing a target species into the fluidic passageof a fluidic device (e.g., a microfluidic device) as disclosed herein,wherein said supplying is configured to cause at least some of thetarget species to bind to the at least one functionalization material;inducing a bulk acoustic wave in the active region; and sensing a changein at least one of a frequency property, a magnitude property, or aphase property of the bulk acoustic wave resonator structure to indicateat least one of presence or quantity of target species bound to the atleast one functionalization material.

In another aspect, a micro-electrical-mechanical system (MEMS) resonatordevice includes a substrate; a bulk acoustic wave resonator structurearranged over at least a portion of the substrate, and at least onefunctionalization material. The bulk acoustic wave resonator structureincludes a piezoelectric material, a top side electrode arranged over aportion of the piezoelectric material, and a bottom side electrodearranged between the piezoelectric material and the substrate, wherein aportion of the piezoelectric material is arranged between the top sideelectrode and the bottom side electrode to form an active region. The atleast one functionalization material is arranged over at least a portionof the active region, wherein less than an entirety of the piezoelectricmaterial is overlaid with the at least one functionalization material.In certain embodiments, the piezoelectric material comprises a hexagonalcrystal structure piezoelectric material (e.g., aluminum nitride or zincoxide) that comprises a c-axis having an orientation distribution thatis predominantly non-parallel to normal of a face of the substrate. Incertain embodiments, one or more portions of the piezoelectric materialmay be overlaid with a hermeticity layer, an interface layer, a SAM,and/or a blocking material as disclosed herein. In certain embodiments,a sensor and/or a fluidic device as disclosed herein may include theforegoing MEMS resonator device.

In another aspect, a method for fabricating amicro-electrical-mechanical system (MEMS) resonator device includesmultiple steps. One step includes forming a bulk acoustic wave resonatorstructure including a piezoelectric material, a top side electrodearranged over a portion of the piezoelectric material, and a bottom sideelectrode arranged between the piezoelectric material and a substrate,wherein a portion of the piezoelectric material is arranged between thetop side electrode and the bottom side electrode to form an activeregion. Another step includes depositing an interface layer over atleast a portion of the active region, and wherein less than an entiretyof the piezoelectric material is overlaid with interface layer material(e.g., comprising a hydroxylated oxide surface, or comprising gold oranother noble metal) available to receive a self-assembled monolayer(SAM). Another step includes forming a self-assembled monolayer over atleast a portion of the interface layer, wherein at least a portion ofthe self-assembled monolayer is arranged over the active region.

In certain embodiments, the method further includes applying a patternedmask over at least a portion of the bulk acoustic wave resonatorstructure prior to the depositing of the interface layer. In certainembodiments, the method further includes depositing at least onefunctionalization material over at least a portion of the self-assembledmonolayer, wherein the at least one functionalization material isregistered with at least a portion of the active region. In certainembodiments, the depositing of the interface layer comprises at leastone of chemical vapor deposition, atomic layer deposition, or physicalvapor deposition. In certain embodiments, the top side electrodecomprises a non-noble metal, and the method further comprises depositinga hermeticity layer between at least portions of the interface layer andthe top side electrode, wherein the hermeticity layer comprises anoxide, a nitride, or an oxynitride dielectric material, and wherein thehermeticity layer comprises a water vapor transmission rate of nogreater than 0.1 (g/m²/day). In certain embodiments, the method furthercomprises depositing a patterned blocking layer over at least oneportion of the interface layer. In certain embodiments, such a patternedblocking layer may comprise at least one of Si₃N₄, SiC, photoresist(e.g., SU-8), polyimide, parylene, or poly(ethylene glycol). In certainembodiments, the method further comprises forming at least one wall overa portion of the bulk acoustic wave resonator structure and defining afluidic passage containing the active region. Preferably, the fluidicpassage may be covered with a cover or cap layer.

In another aspect, any of the foregoing aspects, and/or various separateaspects and features as described herein, may be combined for additionaladvantage. Any of the various features and elements as disclosed hereinmay be combined with one or more other disclosed features and elementsunless indicated to the contrary herein.

Those skilled in the art will appreciate the scope of the presentdisclosure and realize additional aspects thereof after reading thefollowing detailed description of the preferred embodiments inassociation with the accompanying drawing figures.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawing figures incorporated in and forming a part ofthis specification illustrate several aspects of the disclosure, andtogether with the description serve to explain the principles of thedisclosure.

FIG. 1 is a schematic cross-sectional view of a portion of a MEMSresonator device useable with embodiments disclosed herein, including anactive region with a piezoelectric material between overlapping portionsof a top side electrode and a bottom side electrode.

FIG. 2 is a schematic cross-sectional view of an upper portion of a MEMSresonator device according to one embodiment of the present disclosure,including a top side electrode overlaid with a hermeticity layer, aninterface layer, a self-assembled monolayer, and a functionalizationlayer (e.g., specific binding material).

FIG. 3 is a schematic cross-sectional view of a microfluidic deviceincorporating a bulk acoustic wave MEMS resonator device including topside electrode and piezoelectric material surfaces overlaid with ahermeticity layer, an interface layer, a self-assembled monolayer (SAM)arranged over the interface layer, and functionalization (e.g., specificbinding) material and blocking material arranged over first and secondportions of the SAM, respectively, wherein the functionalizationmaterial extends beyond an active region of the MEMS resonator device.

FIG. 4 is a schematic cross-sectional view of a portion of a MEMSresonator device including top side electrode and piezoelectric materialsurfaces overlaid with a hermeticity layer, and with an interface layerpatterned over a portion of the hermeticity layer to cover an activeregion of the MEMS resonator device, according to one embodiment of thepresent disclosure.

FIG. 5 is a schematic cross-sectional view of the MEMS resonator deviceportion of FIG. 4 following application of a self-assembled monolayer(SAM) over the interface layer to cover the active region of the MEMSresonator device, according to one embodiment of the present disclosure.

FIG. 6 is a schematic cross-sectional view of the MEMS resonator deviceportion of FIG. 5 following application of a functionalization (e.g.,specific binding) material over the self-assembled monolayer (SAM) tocover the active region of the MEMS resonator device, according to oneembodiment of the present disclosure.

FIG. 7 is a schematic cross-sectional view of a microfluidic deviceincorporating a bulk acoustic wave MEMS resonator device according toFIG. 6, with walls defining lateral boundaries and with a cover or caplayer defining an upper boundary of a microfluidic channel containingthe active region of the MEMS resonator device, according to oneembodiment of the present disclosure.

FIG. 8 is a schematic cross-sectional view of the microfluidic device ofFIG. 7, following supply of liquid to the microfluidic channel to causea target species to be bound to the functionalization (e.g., specificbinding) material.

FIG. 9 is a schematic cross-sectional view of a microfluidic deviceincorporating a bulk acoustic wave MEMS resonator device according toFIG. 1, with top side electrode and piezoelectric material surfacesoverlaid with a hermeticity layer, with an interface layer patternedover a portion of the hermeticity layer to cover less than an entiretyof an active region of the MEMS resonator device, and withfunctionalization (e.g., specific binding) material arranged over theinterface layer, according to one embodiment of the present disclosure

FIG. 10 is a schematic cross-sectional view of a MEMS resonator deviceportion according to FIG. 1, following deposition of hermeticity andinterface layers over top side electrode and piezoelectric materialsurfaces, with a blocking material layer patterned over portions of theinterface layer non-coincident with the active region of the MEMSresonator device, according to one embodiment of the present disclosure.

FIG. 11 is a schematic cross-sectional view of a microfluidic deviceincorporating a bulk acoustic wave MEMS resonator device according toFIG. 10, with a self-assembled monolayer and a functionalization (e.g.,specific binding) material arranged over the interface layer coincidentwith the entire active region of the MEMS resonator device, with atarget species bound to the functionalization material, and with wallsdefining lateral boundaries and with a cover or cap layer defining anupper boundary of a microfluidic channel containing the active region,according to one embodiment of the present disclosure.

FIG. 12 is a schematic cross-sectional view of a microfluidic deviceincorporating a bulk acoustic wave MEMS resonator device similar to thedevice of FIG. 10, with a blocking material layer patterned over theinterface layer including portions coincident with the active region,with a self-assembled monolayer and a functionalization (e.g., specificbinding) material arranged over a central portion of the active region,with a target species bound to the functionalization material, and withwalls defining lateral boundaries and with a cover or cap layer definingan upper boundary of a microfluidic channel containing the activeregion, according to one embodiment of the present disclosure.

FIG. 13 is a schematic cross-sectional view of a portion of a MEMSresonator device including an inert (e.g., noble metal) top sideelectrode, and including an interface layer and a self-assembledmonolayer arranged over the top side electrode coincident with an activeregion of the MEMS resonator device, according to one embodiment of thepresent disclosure.

FIG. 14 is a schematic cross-sectional view of a microfluidic deviceincorporating the bulk acoustic wave MEMS resonator device of FIG. 13,with functionalization (e.g., specific binding) material arranged overthe interface layer, with a target species bound to thefunctionalization material, and with walls and a cover or cap layerdefining lateral boundaries and an upper boundary, respectively, of amicrofluidic channel containing the active region, according to oneembodiment of the present disclosure.

FIG. 15 is a schematic cross-sectional view of a microfluidic deviceincorporating a bulk acoustic wave MEMS resonator device, with aninterface layer and functionalization (e.g., specific binding) materialarranged over a central portion of a top electrode coincident with acentral portion of an active region, with a target species bound to thefunctionalization material, and with walls and a cover or cap layerdefining lateral boundaries and an upper boundary, respectively, of amicrofluidic channel containing the active region, according to oneembodiment of the present disclosure.

FIG. 16 is a top plan view photograph of a bulk acoustic wave MEMSresonator device suitable for receiving a hermeticity layer, aninterface layer, a self-assembled monolayer, and functionalization (e.g.specific binding) material as disclosed herein.

FIG. 17 is a perspective assembly view of a microfluidic deviceincorporating a substrate with multiple bulk acoustic wave MEMSresonator devices as disclosed herein, an intermediate layer defining achannel containing active regions of the MEMS resonator devices, and acover or cap layer.

FIG. 18 is a schematic cross-sectional view of a film bulk acoustic waveresonator (FBAR) structure usable in devices according to certainembodiments, with the FBAR structure including an inclined c-axishexagonal crystal structure piezoelectric material, a substrate defininga cavity covered by a support layer, and an active region registeredwith the cavity with a portion of the piezoelectric material arrangedbetween overlapping portions of a top side electrode and a bottom sideelectrode.

DETAILED DESCRIPTION

Embodiments set forth below represent the necessary information toenable those skilled in the art to practice the invention and illustratethe best mode of practicing the invention. Upon reading the followingdescription in light of the accompanying drawing figures, those skilledin the art will understand the concepts of the invention and willrecognize applications of these concepts not particularly addressedherein. It should be understood that these concepts and applicationsfall within the scope of the disclosure and the accompanying claims.

It will be understood that, although the terms first, second, etc. maybe used herein to describe various elements, these elements should notbe limited by these terms. These terms are only used to distinguish oneelement from another. For example, a first element could be termed asecond element, and, similarly, a second element could be termed a firstelement, without departing from the scope of the present disclosure. Asused herein, the term “and/or” includes any and all combinations of oneor more of the associated listed items.

Relative terms such as “below” or “above” or “upper” or “lower” or“horizontal” or “vertical” may be used herein to describe a relationshipof one element, layer, or region to another element, layer, or region asillustrated in the Figures. It will be understood that these terms andthose discussed above are intended to encompass different orientationsof the device in addition to the orientation depicted in the Figures.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the disclosure.As used herein, the singular forms “a,” “an,” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises,”“comprising,” “includes,” and/or “including” when used herein specifythe presence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof. As used herein, the terms “proximate”and “adjacent” as applied to a specified layer or element refer to astate of being close or near to another layer or element, and encompassthe possible presence of one or more intervening layers or elementswithout necessarily requiring the specified layer or element to bedirectly on or directly in contact with the other layer or elementunless specified to the contrary herein.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this disclosure belongs. It willbe further understood that terms used herein should be interpreted ashaving a meaning that is consistent with their meaning in the context ofthis specification and the relevant art and will not be interpreted inan idealized or overly formal sense unless expressly so defined herein.

The present disclosure relates in one aspect to amicro-electrical-mechanical system (MEMS) resonator device arranged on asubstrate, the MEMS resonator device including a piezoelectric material,an interface layer, and a self-assembled monolayer (SAM) suitable forbiological functionalization (e.g., by receiving at least one specificbinding material) arranged over at least a portion of an active regionof the device, wherein less than an entirety of the piezoelectricmaterial is overlaid with interface layer material that is available toreceive a self-assembled monolayer. In certain embodiments, theinterface layer is arranged over less than an entirety of thepiezoelectric material, or a patterned blocking layer (e.g., at leastone of Si₃N₄, SiC, photoresist (e.g., SU-8), polyimide, parylene, orpolyethylene glycol) is arranged over at least a portion of theinterface layer whereby presence of the patterned blocking materialrenders a portion of the interface layer unavailable to receive a SAM.Deposition techniques such as atomic layer deposition (ALD), chemicalvapor deposition (CVD), or physical vapor deposition (PVD) may be usedin conjunction with one or more masks (e.g., photolithographic masks) topattern the interface layer over selected portions (i.e., less than theentirety) of a MEMS resonator device, including at least a portion of anactive region. The interface layer preferably comprises a materialsuitable for attachment of an organosilane-based SAM. By pre-defining apatterned interface layer with a high dimensional tolerance (i.e.,either the interface layer itself, or by covering one or more regions ofthe interface layer with blocking material), forming a SAM registeredwith the interface layer, and then applying a functionalization (e.g.,specific binding) material to the SAM, a higher dimensional tolerancemay be achieved for positioning of the functionalization material thancould be attained by microarray spotting alone. In this manner,alignment and overprinting challenges of microarray spotting can beovercome by improved patterning of underlying layers (i.e., an interfacelayer and SAM).

A preferred micro-electrical-mechanical system (MEMS) resonator deviceaccording to certain embodiments includes a substrate, a bulk acousticwave resonator structure arranged over at least a portion of thesubstrate, an interface layer, and a self-assembled monolayer (SAM). Incertain embodiments of the present disclosure, an interface layer isarranged over at least a portion of the active region but arranged overless than an entirety of a piezoelectric material, and the SAM beingarranged over at least a portion of the interface layer. In otherembodiments, an interface layer is provided over a larger area(optionally spanning over an entire piezoelectric material), and apatterned blocking layer (e.g., at least one of Si₃N₄, SiC, photoresist(e.g., SU-8), polyimide, parylene, or polyethylene glycol) is arrangedover at least a portion of the interface layer, whereby presence of thepatterned blocking material renders a portion of the interface layerunavailable to receive a SAM. In certain embodiments, the interfacelayer comprises a hydroxylated oxide surface, and the self-assembledmonolayer comprises an organosilane material. In certain embodiments,the interface layer comprises gold or another noble metal, and theself-assembled monolayer comprises a thiol material.

FIG. 1 is a schematic cross-sectional view of a portion of a bulkacoustic wave MEMS resonator device that is devoid of overlying layersbut useable with embodiments disclosed herein. The bulk acoustic waveMEMS resonator device 10 includes a substrate 12 (e.g., typicallysilicon or another semiconductor material), an acoustic reflector 14arranged over the substrate 12, a piezoelectric material 22, and bottomand top side electrodes 20, 28. The bottom side electrode 20 is arrangedalong a portion of a lower surface 24 of the piezoelectric material 22(between the acoustic reflector 14 and the piezoelectric material 22),and the top side electrode 28 is arranged along a portion of an uppersurface 26 of the piezoelectric material 22. An area in which thepiezoelectric material 22 is arranged between overlapping portions ofthe top side electrode 28 and the bottom side electrode 20 is consideredthe active region 30 of the resonator device 10. The acoustic reflector14 serves to reflect acoustic waves and therefore reduce or avoid theirdissipation in the substrate 12. In certain embodiments, an acousticreflector 14 includes alternating thin layers 16, 18 of differentmaterials (e.g., silicon oxicarbide [SiOC], silicon nitride [Si₃N₄],silicon dioxide [SiO₂], aluminum nitride [AlN], tungsten [W], andmolybdenum [Mo]), optionally embodied in a quarter-wave Bragg mirror,deposited over the substrate 12. In certain embodiments, other types ofacoustic reflectors may be used. Steps for forming the resonator device10 may include depositing the acoustic reflector 14 over the substrate12, followed by deposition of the bottom side electrode 20, followed bygrowth (e.g., via sputtering or other appropriate methods) of thepiezoelectric material 22, followed by deposition of the top sideelectrode 28.

In certain embodiments, an interface layer is patterned or otherwiseavailable to receive a SAM over an entirety of an active region of aMEMS resonator device, to permit a SAM and functionalization (e.g.,specific binding) material applied over the interface layer to overlapthe entire active region. In other embodiments, a blocking layer ispatterned over an interface layer, or only a portion of the interfacelayer is otherwise available to receive a SAM, over only a portion of anactive region, to permit the SAM and functionalization material appliedover the interface layer to overlap only a portion of the active region.

In certain embodiments, photolithography may be used to promotepatterning of interface material or blocking material over portions of aMEMS resonator device. Photolithography involves use of light totransfer a geometric pattern from a photomask to a light-sensitivechemical photoresist on a substrate, and is a process well known tothose of ordinary skill in the semiconductor fabrication art. Typicalsteps employed in photolithography include wafer cleaning, photoresistapplication (involving either positive or negative photoresist), maskalignment, and exposure and development. After features are defined inphotoresist on a desired surface, an interface layer may be patterned byetching in one or more gaps in a photoresist layer, and the photoresistlayer may be subsequently removed (e.g., using a liquid photoresiststripper, by ashing via application of an oxygen-containing plasma, oranother removal process).

In certain embodiments, an interface layer includes a hydroxylated oxidesurface suitable for formation of an organosilane SAM layer. A preferredinterface layer material including a hydroxylated oxide surface issilicon dioxide [SiO₂]. Alternative materials incorporating hydroxylatedoxide surfaces for forming interface layers include titanium dioxide[TiO₂] and tantalum pentoxide [Ta₂O₅]. Other alternative materialsincorporating hydroxylated oxide surfaces will be known to those skilledin the art, and these alternatives are considered to be within the scopeof the present disclosure.

In other embodiments, an interface layer includes gold or another noblemetal (e.g., ruthenium, rhodium, palladium, osmium, iridium, platinum,or silver) suitable for receiving a thiol-based SAM.

In certain embodiments incorporating electrode materials subject tocorrosion, a hermeticity layer may also be applied between a top sideelectrode and the interface layer. A hermeticity layer may beunnecessary when noble metals (e.g., gold, platinum, etc.) are used fortop side electrodes. If provided, a hermeticity layer preferablyincludes a dielectric material with a low water vapor transmission rate(e.g., no greater than 0.1 (g/m²/day)). Following deposition of theselayers, a SAM may be formed over the interface layer, with the SAMpreferably including an organosilane material. The hermeticity layerprotects a reactive electrode material (e.g., aluminum or aluminumalloy) from attack in corrosive liquid environments, and the locallypatterned interface layer facilitates proper chemical binding of theSAM.

In certain embodiments, a hermeticity layer and/or an interface layermay be applied via one or more deposition processes such as atomic layerdeposition (ALD), chemical vapor deposition (CVD), or physical vapordeposition (PVD). Of the foregoing processes, ALD is preferred fordeposition of at least the hermeticity layer (and may also be preferablefor deposition of the interface layer), due to its ability to provideexcellent conformal coating with good step coverage over devicefeatures, so as to provide layer structures that are free of pinholes.Moreover, ALD is capable of forming uniformly thin layers that providerelatively little damping of acoustic vibrations that would otherwiseresult in degraded device performance. Adequacy of coverage is importantfor a hermeticity layer (if present) to avoid corrosion of theunderlying electrode. If ALD is used for deposition of a hermeticitylayer, then in certain embodiments a hermeticity layer may include athickness in a range of from about 10 nm to about 25 nm. In certainembodiments, hermeticity layer thickness is about 15 nm, or from about12 nm to about 18 nm. Conversely, if another process such as CVD isused, then a hermeticity layer may include a thickness in a range offrom about 80 nm to about 150 nm or more, or in a range of from about 80nm to about 120 nm. Considering both of the foregoing processes,hermeticity layer thicknesses may range from about 5 nm to about 150 nm.If ALD is used for deposition of an interface layer, then an interfacelayer may include a thickness in a range of from about 5 nm to about 15nm. In certain embodiments, an interface layer may include a thicknessof about 10 nm, or in a range of from about 8 nm to about 12 nm. Otherinterface layer thickness ranges and/or deposition techniques other thanALD may be used in certain embodiments. In certain embodiments, ahermeticity layer and an interface layer may be sequentially applied ina vacuum environment, thereby promoting a high-quality interface betweenthe two layers.

If provided, a hermeticity layer may include an oxide, a nitride, or anoxynitride material serving as a dielectric material and having a lowwater vapor transmission rate (e.g., no greater than 0.1 (g/m²/day))according to certain embodiments. In certain embodiments, thehermeticity layer includes at least one of Al₂O₃ or SiN. In certainembodiments, the interface layer includes at least one of SiO₂, TiO₂, orTa₂O₅. In certain embodiments, multiple materials may be combined in asingle hermeticity layer, and/or a hermeticity layer may includemultiple sublayers of different materials. Preferably, a hermeticitylayer is further selected to promote compatibility with an underlyingreactive metal (e.g., aluminum or aluminum alloy) electrode structure ofan acoustic resonator structure. Although aluminum or aluminum alloysare frequently used as electrode materials in bulk acoustic waveresonators, various transition and post-transition metals can be usedfor such electrodes.

Following deposition of an interface layer (optionally arranged over anunderlying hermeticity layer), a SAM is preferably formed over theinterface layer. SAMs are typically formed by exposure of a solidsurface to amphiphilic molecules with chemical groups that exhibitstrong affinities for the solid surface. When an interface layercomprising a hydroxylated oxide surface is used, then organosilane SAMlayers are particularly preferred for attachment to the hydroxylatedoxide surface. Organosilane SAMs promote surface bonding throughsilicon-oxygen (Si—O) bonds. More specifically, organosilane moleculesinclude a hydrolytically sensitive group and an organic group, and aretherefore useful for coupling inorganic materials to organic polymers.An organosilane SAM may be formed by exposing a hydroxylated surface toan organosilane material in the presence of trace amounts of water toform intermediate silanol groups. These groups then react with freehydroxyl groups on the hydroxylated surface to covalently immobilize theorganosilane. Examples of possible organosilane-based SAMs that arecompatible with interface layers incorporating hydroxylated oxidesurfaces include 3-glycidoxypropyltrimethoxysilane (GPTMS),3-mercaptopropyltrimethoxysilane (MPTMS), 3-aminopropyltrimethoxysilane(APTMS), and octadecyltrimethoxysilane (OTMS), including their ethoxy-and chloro-variants. Additional silanes that may be used for SAMsinclude poly(ethylene glycol) (PEG) conjugated variants. Those skilledin the art will recognize that other alternatives exist, and thesealternatives are considered to be within the scope of the presentdisclosure. An exemplary SAM may include a thickness in a range of atleast 0.5 nm or more. Preferably, a SAM readily binds to the locallypatterned interface layer, but does not readily bind to other adjacentmaterial layers (e.g., a hermeticity layer, a piezoelectric material,and/or a blocking material layer).

When an interface layer comprising gold or another noble metal is used,then thiol-based (e.g., alkanethiol-based) SAM layers may be used.Alkanethiols are molecules with an alkyl chain as the back bone, a tailgroup, and a S—H head group. Thiols may be used on noble metal interfacelayers due to the strong affinity of sulfur for these metals. Examplesof thiol-based SAMs that may be used include, but are not limited to,1-dodecanethiol (DDT), 11-mercaptoundecanoic acid (MUA), andhydroxyl-terminated (hexaethylene glycol) undecanethiol (1-UDT). Thesethiols contain the same backbone, but different end groups—namely,methyl (CH₃), carboxyl (COOH), and hydroxyl-terminated hexaethyleneglycol (HO—(CH₂CH₂O)₆) for DDT, MUA, and 1-UDT, respectively. In certainembodiments, SAMs may be formed by incubating gold surfaces in thiolsolutions using a suitable solvent, such as anhydrous ethanol.

Following formation of a SAM, the SAM may be biologicallyfunctionalized, such as by receiving at least one functionalization(e.g., specific binding) material. In certain embodiments, specificbinding materials may be applied on or over a SAM using a microarrayspotting needle or other suitable methods. Since a SAM and an underlyinginterface layer are patterned (e.g., using photolithography for definingthe interface layer) with a high dimensional tolerance over only aportion of a resonator structure (which includes a substrate), and thesubsequently applied specific binding material preferably attaches onlyto the SAM, a higher dimensional tolerance may be achieved forpositioning of the specific binding material than could be attained bymicroarray spotting alone. Examples of specific binding materialsinclude, but are not limited to, antibodies, receptors, ligands, and thelike. A specific binding material is preferably configured to receive apredefined target species (e.g., molecule, protein, DNA, virus,bacteria, etc.). A functionalization layer including specific bindingmaterial may include a thickness in a range of from about 5 nm to about1000 nm, or from about 5 nm to about 500 nm. In certain embodiments, anarray of different specific binding materials may be provided overdifferent active areas of a multi-resonator device (i.e., a resonatordevice including multiple active areas), optionally in combination withone or more active areas that are devoid of specific binding materialsto serve as comparison (or “reference”) regions. In certain embodiments,a functionalization material may provide non-specific binding utility.

Certain embodiments are directed to a fluidic device including multiplebulk acoustic wave MEMS resonator structures as disclosed herein andincluding a fluidic passage (e.g., a channel, a chamber, or the like)arranged to conduct a liquid to contact at least one functionalization(e.g., specific binding) material arranged over at least one activeregion of the resonator structures. Such a device may be microfluidic inscale, and comprise at least one microfluidic passage (e.g., having atleast one dimension, such as height and/or width, of no greater thanabout 500 microns, or about 250 microns, or about 100 microns). Forexample, following fabrication of bulk acoustic wave MEMS resonatorstructures and deposition of a SAM over portions thereof (optionallypreceded by deposition of a hermeticity layer and an interface layer), amicrofluidic device may be fabricated by forming one or more wallsdefining lateral boundaries of a microfluidic passage over a first bulkacoustic wave MEMS resonator structure with an active region thereofarranged along a bottom surface of the microfluidic passage, and thenenclosing the microfluidic passage using a cover or cap layer that maydefine fluidic ports (e.g., openings) enabling fluid communication withthe microfluidic passage. In certain embodiments, functionalization(e.g., specific binding) material may be pre-applied to the activeregion of a bulk acoustic wave MEMS resonator structure before formationof a microfluidic passage; in other embodiments, functionalizationmaterial may be applied over an active region of a bulk acoustic waveresonator structure following formation of the microfluidic passage.

An example of a MEMS resonator device overlaid with multiple layers forproviding biosensing utility according to one embodiment is provided inFIG. 2. FIG. 2 is a schematic cross-sectional view of an upper portionof a MEMS resonator device including a piezoelectric material 22 and atop side electrode 28, wherein at least the top side electrode 28 isoverlaid with a hermeticity layer 32, an interface layer 34, aself-assembled monolayer 36, and a functionalization layer (e.g.,specific binding material) 38. In certain embodiments, the MEMSresonator device includes a bulk acoustic wave resonator device, and thepiezoelectric material 22 includes aluminum nitride or zinc oxidematerial that includes a c-axis having an orientation distribution thatis predominantly non-parallel (and may also be non-perpendicular) tonormal of a face of the substrate. Such a c-axis orientationdistribution enables creation of shear displacements, which beneficiallyenable operation of the MEMS resonator device with liquids, such as in asensor and/or microfluidic device. In certain embodiments, piezoelectricmaterial includes a c-axis with a longitudinal orientation.

Methods for forming hexagonal crystal structure piezoelectric materialsincluding a c-axis having an orientation distribution that ispredominantly non-parallel to normal of a face of a substrate aredisclosed in U.S. patent application Ser. No. 15/293,063 filed on Oct.13, 2016, with the foregoing application hereby being incorporated byreference herein. Additional methods for forming piezoelectric materialshaving an inclined c-axis orientation are disclosed in U.S. Pat. No.4,640,756 issued on Feb. 3, 1987, with the foregoing patent hereby beingincorporated by reference herein.

Certain embodiments are directed to a fluidic device (e.g., amicrofluidic device) including a MEMS resonator device as disclosedherein and including a fluidic passage (e.g., a channel, a chamber, orthe like) arranged to conduct a liquid to contact at least onefunctionalization material. For example, following fabrication of a MEMSresonator device and deposition of an interface layer and a SAM overportions thereof (optionally preceded by deposition of a hermeticitylayer), a microfluidic device may be fabricated by forming one or morewalls defining lateral boundaries of a microfluidic channel preferablycontaining the active region of at least one acoustic resonator,followed by application of a cover or cap layer to enclose themicrofluidic channel. In certain embodiments, functionalization (e.g.,specific binding) material may be applied after formation of walls of amicrofluidic channel, but prior to application of the cover or caplayer. Walls of a microfluidic channel may be formed of any suitablematerial, such as laser-cut “stencil” layers of thin polymeric materialsand/or laminates, optionally including one or more self-adhesivesurfaces (e.g., adhesive tape). Optionally such walls may be formedprior to deposition of a SAM layer, a functionalization layer, and/orblocking layers, with an SU-8 negative epoxy resist or other photoresistmaterial. A cover or cap layer of a microfluidic device may be formed bydefining ports (e.g., via laser cutting or water jet cutting) in a layerof an appropriate material (e.g., preferably a substantially inertpolymer, glass, silicon, ceramic, or the like), and adhering the coveror cap layer to top surfaces of the walls.

As indicated previously herein, it may be difficult to achieve a highdegree of alignment between functionalization material and an activeregion of a MEMS resonator device through reliance on microarrayspotting. FIG. 3 is a schematic cross-sectional view of a microfluidicdevice 50 incorporating a bulk acoustic wave MEMS resonator deviceincluding top side electrode 28 and piezoelectric material 22 surfacesoverlaid with a hermeticity layer 32, an interface layer 34, aself-assembled monolayer (SAM) 36 arranged over the interface layer 34,and functionalization (e.g., specific binding) material 38 and chemicalor biological blocking material (e.g., a blocking buffer) 40 arrangedover first and second (i.e., central and peripheral) portions of the SAM36, respectively. The hermeticity layer 32, the interface layer 34, andthe SAM 36 extend over substantially the entirety of a substrate 12;however, the chemical or biological blocking material 40 (which isnon-coincident with an active region 30) locally prevents adhesion offunctionalization material 38 to the interface layer 34.

The proper choice of a chemical or biological blocking material (e.g.,blocking buffer) for a given analysis depends on the type of targetspecies or analyte present in a sample. Various types of blockingbuffers such as highly purified proteins, serum, or milk may be used toblock free sites on a monolayer. Additional blockers includeethanolamine or polyethylene oxide (PEO) containing materials. An idealblocking buffer would bind to all potential sites of nonspecificinteraction away from an active region. To optimize a blocking bufferfor a particular analysis, empirical testing may be used to determinesignal-to-noise ratio. No single chemical blocking material is ideal forevery situation, since each antibody-antigen pair has uniquecharacteristics.

In FIG. 3, a target species 42 is bound to the functionalizationmaterial 38. The MEMS resonator device further includes the substrate12, an acoustic reflector 14, and a bottom side electrode 20 arrangedbelow the piezoelectric material 22. Walls 44 that are laterallydisplaced from the active region 30 extend upward (e.g., above the SAM36) to define lateral boundaries of a microfluidic channel 52 containingthe active region 30. If the walls 44 are formed on the SAM 36, the SAM36 may promote adhesion of the walls 44. Such walls may be formed of anysuitable material, such as a laser-cut “stencil” layer of thin polymericmaterials and/or laminate materials, optionally including one or moreself-adhesive surfaces (e.g. adhesive tape). Optionally such walls maybe formed prior to deposition of a SAM, functionalization and blockinglayers with an SU-8 negative epoxy resist or other photoresist material.A cover 46 defining fluidic ports 48A, 48B is further provided toprovide an upper boundary for the microfluidic channel 52.

As shown in FIG. 3, a laterally extending portion 38A of thefunctionalization material 38 extends laterally beyond the active region30 of the MEMS resonator device, and a portion 42A of the target species42 is bound to the laterally extending portion 38A of thefunctionalization material 38. This laterally extending portion 38A ofthe functionalization material 38 constitutes excess functionalization(e.g., specific binding) material that may reduce sensor response, suchas by impairing a lower limit of detection. Moreover, the excessfunctionalization material 38A is also arranged asymmetrically relativeto the active region 30. The presence of excess functionalizationmaterial 38A misaligned with the active region 30 may be undesirable,giving rise to the subject matter of the present application in which apatterned interface layer with a high dimensional tolerance is appliedover a MEMS resonator structure, a SAM is subsequently formed registeredwith the interface layer, and a functionalization (e.g., specificbinding) material is applied to the SAM, as described in connection withvarious embodiments that follow.

FIG. 4 is a schematic cross-sectional view of a portion of a MEMSresonator device similar to the device of FIG. 1 (including a substrate12, an acoustic reflector 14, a piezoelectric material 22, bottom andtop side electrodes 20, 28), but with surfaces of the top side electrode28 and the piezoelectric material 22 being overlaid with a hermeticitylayer 32, and with an interface layer 34 patterned over a centralportion of the hermeticity layer 32 to cover an active region 30 of theMEMS resonator device, according to one embodiment of the presentdisclosure. The interface layer 34 preferably comprises a hydroxylatedoxide surface, or a gold or other noble metal, suitable for receiving aSAM. In certain embodiments, the interface layer 34 may be patternedover a portion of the MEMS resonator device (e.g., to cover only aportion of the substrate 12) using a photomask (not shown). As shown,the interface layer 34 may cover an entire horizontal top surface aswell as (e.g., vertical) step surfaces of the top side electrode 28, butdoes not extend laterally a significant distance away from the activeregion 30.

FIG. 5 is a schematic cross-sectional view of the MEMS resonator deviceportion of FIG. 4 following application of a self-assembled monolayer(SAM) 36 over the interface layer 34 to cover the active region 30 ofthe MEMS resonator device, according to one embodiment of the presentdisclosure. In certain embodiments, the SAM 36 comprises an organosilanematerial. The remaining elements of FIG. 5 are identical to thosedisclosed in connection with FIG. 4. Since the interface layer 34 islocally patterned over a central portion of the MEMS resonator device,the SAM 36 preferably adheres to the interface layer 34 (e.g., SiO₂) butnot to the hermeticity layer 32 (e.g., SiN), less than an entirety ofthe piezoelectric material 22 is overlaid with interface layer materialthat is available to receive a SAM. Moreover, the need for a chemical orbiological blocking material (e.g., material 40 as shown in FIG. 3) toprevent subsequent deposition of functionalization material 38 away fromthe active region 30 may be avoided.

FIG. 6 is a schematic cross-sectional view of the MEMS resonator deviceportion of FIG. 5 following application of a functionalization (e.g.,specific binding) material 38 over the self-assembled monolayer (SAM) 36(which is arranged over the interface layer 34) to cover the activeregion 30 of the MEMS resonator device, according to one embodiment ofthe present disclosure. The remaining elements of FIG. 6 are identicalto those disclosed in connection with FIGS. 4 and 5. As shown, thefunctionalization material 38 covers an entire horizontal top surface aswell as (e.g., vertical) step surfaces of the top side electrode 28, theSAM 36, and the interface layer 34, but does not extend laterally asignificant distance away from the active region 30. Thefunctionalization material 38 may be “overprinted” to ensure that theentire active region 30 is covered, and thereafter any excessfunctionalization material may be washed away. The zone wherefunctionalization material 38 is present is therefore defined by theprecise process step of patterning the interface layer 34, therebyaddressing issues of misalignment and oversizing of a functionalizationzone that would arise by relying solely on microarray spotting todetermine placement of the functionalization material 38.

FIG. 7 is a schematic cross-sectional view of a microfluidic device 50Aincorporating a bulk acoustic wave MEMS resonator device according toFIG. 6, with walls 44 defining lateral boundaries and with a cover 46defining an upper boundary of a microfluidic channel 52 containing anactive region 30 of the MEMS resonator device, according to oneembodiment of the present disclosure. The cover 46 defines fluidic ports48A, 48B suitable to permit fluid (e.g., liquid) containing a targetspecies to be introduced into the microfluidic channel 52. The MEMSresonator device includes a substrate 12, an acoustic reflector 14arranged over the substrate 12, a piezoelectric material 22, and bottomand top side electrodes 20, 28 arranged under and over regions of thepiezoelectric material 22, respectively. An area in which thepiezoelectric material 22 is arranged between overlapping portions ofthe top side electrode 28 and the bottom side electrode 20 defines theactive region 30. A hermeticity layer 32 is provided over an entirety ofthe top side electrode 28 and the piezoelectric material 22. Aninterface layer 34 is patterned over a central portion of thehermeticity layer 32 including the active region 30, and a SAM 36 islocally provided over the interface layer 34. As shown,functionalization material 38 is arranged over an entire horizontal topsurface as well as (e.g., vertical) step surfaces of the top sideelectrode 28, the SAM 36, and the interface layer 34, but does notextend laterally a significant distance away from the active region 30.Preferably, fabrication of the microfluidic device 50A includesformation of a MEMS resonator according to FIG. 1, followed bydeposition of the hermeticity layer 32, localized deposition of theinterface layer 34 and formation of the SAM 36 over the active region30, formation of the walls 44, deposition of the functionalizationmaterial 38 over the SAM 36, and application of the cover 46.

FIG. 8 is a schematic cross-sectional view of the microfluidic device50A of FIG. 7, following supply of liquid to the microfluidic channel 52(i.e., through one or both fluidic ports 48A, 48B to cause a targetspecies 42 to be bound to the functionalization material 38. In certainembodiments, the functionalization material 38 comprises specificbinding material that is selected to specifically bind the targetspecies 42. In operation, the bulk acoustic wave MEMS resonator deviceis driven with a shear radio frequency to detect the frequency shift ofthe bound target species (or analyte) 42.

In the microfluidic device 50A illustrated in FIGS. 7 and 8, theinterface layer 34, SAM 36, and functionalization material 38 cover theentire active region 30. In alternative embodiments, an interface layer,a SAM, and functionalization material may be arranged over less than anentirety of an active region.

FIG. 9 is a schematic cross-sectional view of a microfluidic device 50Bincorporating a bulk acoustic wave MEMS resonator device according toFIG. 1, with functionalization (e.g., specific binding) material 38, aSAM 36, and an interface layer 34 arranged over less than an entirety ofan active region 30. The MEMS resonator device includes a substrate 12,an acoustic reflector 14, a bottom side electrode 20 arranged below aportion of the piezoelectric material 22, and a top side electrode 28arranged over a portion of the piezoelectric material 22, wherein anarea in which the piezoelectric material 22 is arranged betweenoverlapping portions of the top side electrode 28 and the bottom sideelectrode 20 defines the active region 30. A hermeticity layer 32 isarranged over (e.g., the entirety of) the top side electrode 28 and thepiezoelectric material 22. After formation of the hermeticity layer 32,an interface layer 34 is patterned over a portion of the hermeticitylayer 32, overlying a portion (but less than an entirety) of the activeregion 30. Thereafter, a SAM 36 is formed over the interface layer 34.Following formation of the SAM 36, walls 44 may be formed to definelateral boundaries of a microfluidic channel 52 containing the activeregion 30 (e.g., with the walls 44 being laterally displaced from theactive region 30), and the functionalization material 38 is applied tothe SAM 36 (e.g., by microarray spotting). Thereafter, a cover 46 isapplied to top surfaces of the walls 44, with the cover 46 definingfluidic ports 48A, 48B suitable to permit fluid (e.g., liquid)containing a target species 42 to be introduced into the microfluidicchannel 52. As shown in FIG. 9, the target species 42 is bound to thefunctionalization material 38, such as may occur after fluid containingthe target species 42 is flowed into the microfluidic channel 52 tocontact the functionalization material 38. The use of afunctionalization material 38 covering less than an entirety of theactive region 30 may be beneficial to adjust response sensitivity and/ordetection limit of the microfluidic device 50B.

In certain embodiments, a patterned blocking layer (e.g., including oneor more non-oxide thin films such as silicon nitride [Si₃N₄] or siliconcarbide [SiC]; or organic materials such as SU-8, photoresist,polyimide, parylene, or poly(ethylene glycol)) may be arranged over atleast a portion of an interface layer, whereby presence of the patternedblocking material renders a portion of the interface layer unavailableto receive a SAM.

FIG. 10 is a schematic cross-sectional view of a MEMS resonator deviceportion according to FIG. 1 (including a substrate 12, an acousticreflector 14, a piezoelectric material 22, bottom and top sideelectrodes 20, 28), following deposition of a hermeticity layer 32 andan interface layer 34 over surfaces of the top side electrode 28 and thepiezoelectric material 22, and following patterning of a blockingmaterial layer 54 over portions of the interface layer 34 non-coincidentwith an active region 30 of the MEMS resonator device, according to oneembodiment of the disclosure. The zone and area of functionalization isultimately determined by areas of the interface layer 34 exposed by thepatterned blocking material layer 54. The interface layer 34 preferablycomprises a hydroxylated oxide surface, or gold or another noble metal,suitable for receiving a SAM (not shown). In certain embodiments, thehermeticity layer 32 and the interface layer 34 may be provided oversubstantially the entire piezoelectric material 22 and/or the entireMEMS resonator device, but less than an entirety of the piezoelectricmaterial 22 is overlaid with interface layer material that is availableto receive a self-assembled monolayer, due to presence of the blockingmaterial layer 54 overlying portions of the interface layer 34. Incertain embodiments, the blocking material layer 54 includes at leastone of Si₃N₄, SiC, Au, photoresist, polyimide, or parylene. Followingfabrication of the piezoelectric material 22 and electrodes 20, 28, thehermeticity layer 32 and the interface layer 34 may be deposited by anysuitable methods disclosed herein. Thereafter, a patterning techniquesuch as photolithography and selective etching may be used to patternthe blocking material layer 54 with a high degree of precision overportions of the interface layer 34. Following application of theblocking material layer 54, only a central portion of the interfacelayer 34 proximate to the active region 30 is available to receive a SAM(not shown).

FIG. 11 is a schematic cross-sectional view of a microfluidic device 50Cincorporating a bulk acoustic wave MEMS resonator device according toFIG. 10, with a self-assembled monolayer (SAM) 36 and afunctionalization (e.g. specific binding) material 38 arranged over acentral portion of the interface layer 34 overlapping an entire activeregion 30 of the MEMS resonator device. The MEMS resonator devicefurther includes a substrate 12, an acoustic reflector 14, a bottom sideelectrode 20 and a top side electrode 28 adjacent to a piezoelectricmaterial 22, and hermeticity layer 32 arranged over surfaces of thepiezoelectric material 22 and the top side electrode 28. Walls 44 arelaterally displaced from the active region 30 extend upward from ablocking material layer 54, and define lateral boundaries of amicrofluidic channel 52 containing the active region 30. A cover 46 isarranged over top surfaces of the walls 44 and defines fluidic ports48A, 48B suitable to permit fluid (e.g., liquid) containing a targetspecies 42 to be introduced into the microfluidic channel 52. As shownin FIG. 11, the target species 42 is bound to the functionalizationmaterial 38, such as may occur after fluid containing the target species42 is flowed into the microfluidic channel 52 to contact thefunctionalization material 38.

In other embodiments, an interface layer is patterned over a SAM, or isotherwise available to receive a SAM, over only a portion of an activeregion, to permit a SAM and functionalization material applied over theinterface layer to overlap only a portion of the active region.

FIG. 12 is a schematic cross-sectional view of a microfluidic device 50Dincorporating a bulk acoustic wave MEMS resonator device similar to thedevice of FIG. 10, but with a blocking material layer 54 patterned overthe interface layer 34 including portions coincident with (i.e.,overlapping) the active region 30. Only a central portion 34A of theinterface layer 34 includes an upper surface available to receive aself-assembled monolayer (SAM) 36, such that the SAM 36 and overlyingfunctionalization (e.g., specific binding) material 38 are arranged overonly a portion of the active region 30. The MEMS resonator devicefurther includes a substrate 12, an acoustic reflector 14, a bottom sideelectrode 20 and a top side electrode 28 adjacent to a piezoelectricmaterial 22, and a hermeticity layer 32 arranged over the piezoelectricmaterial 22 and the top side electrode 28. Walls 44 are laterallydisplaced from the active region 30, extend upward from the blockingmaterial layer 54, and define lateral boundaries of a microfluidicchannel 52 containing the active region 30. A cover 46 is arranged overtop surfaces of the walls 44 and defines fluidic ports 48A, 48B suitableto permit fluid (e.g., liquid) containing a target species 42 to beintroduced into the microfluidic channel 52. As shown in FIG. 12, thetarget species 42 is bound to the functionalization material 38, such asmay occur after fluid containing the target species 42 is flowed intothe microfluidic channel 52 to contact the functionalization material38.

FIG. 13 a schematic cross-sectional view of a portion of a MEMSresonator device including an inert (e.g., noble metal) top sideelectrode 28 (thereby obviating the need for a hermeticity layer tocover the top side electrode 28), with an interface layer 34 and aself-assembled monolayer (SAM) 36 arranged over the top side electrode28 coincident with an active region 30 of the MEMS resonator device,according to one embodiment of the present disclosure. The MEMSresonator device further includes a substrate 12, an acoustic reflector14, and a bottom side electrode 20 adjacent to a piezoelectric material22. The interface layer 34 may be deposited by any suitable depositiontechnique disclosed herein (e.g., ALD, CVD, or PVD), preferably inconjunction with one or more masks (e.g., photolithographic masks) toprecisely control its placement. The interface layer 34 preferablycomprises a material including a hydroxylated oxide surface suitable forattachment of an organosilane-based SAM, or comprises gold or anothernoble metal suitable for attachment of a thiol-based SAM. Afterformation of the interface layer 34, the self-assembled monolayer (SAM)36 may be deposited thereon.

FIG. 14 is a schematic cross-sectional view of a microfluidic device 50Eincorporating the bulk acoustic wave MEMS resonator device of FIG. 13.Walls 44 are laterally displaced from the active region 30, extendupward from the piezoelectric material 22 and top side electrode 28, anddefine lateral boundaries of a microfluidic channel 52 containing theactive region 30. A cover 46, arranged over top surfaces of the walls44, defines a top boundary of the microfluidic channel 52, and definesfluidic ports 48A, 48B suitable to permit fluid (e.g., liquid)containing a target species 42 to be introduced into the microfluidicchannel 52. As shown in FIG. 14, functionalization (e.g., specificbinding) material 38 is arranged over the SAM 36 and the interface layer34, and the target species 42 is bound to the functionalization material38, such as may occur after fluid containing the target species 42 isflowed into the microfluidic channel 52 to contact the functionalizationmaterial 38.

FIG. 15 is a schematic cross-sectional view of a microfluidic device 50Fincorporating a bulk acoustic wave MEMS resonator device, with aninterface layer 34, a SAM 36, and a functionalization (e.g., specificbinding) material 38 arranged over only a portion of an active region 30of the MEMS resonator device. The MEMS resonator device further includesa substrate 12, an acoustic reflector 14, and a bottom side electrode 20and a top side electrode 28 adjacent to a piezoelectric material 22,wherein an area in which the piezoelectric material 22 is arrangedbetween overlapping portions of the top side electrode 28 and the bottomside electrode 20 is considered the active region 30. The interfacelayer 34 may be deposited by any suitable deposition technique disclosedherein (e.g., ALD, CVD, or PVD), preferably in conjunction with one ormore masks (e.g., photolithographic masks) to precisely control itsplacement. The interface layer 34 preferably comprises a materialincluding a hydroxylated oxide surface suitable for attachment of anorganosilane-based SAM, or comprises gold or another noble metalsuitable for attachment of a thiol-based SAM. Walls 44 are laterallydisplaced from the active region 30, extend upward from thepiezoelectric material 22 and top side electrode 28, and define lateralboundaries of a microfluidic channel 52 containing the active region 30.A cover 46 arranged over top surfaces of the walls 44 defines a topboundary of the microfluidic channel 52, and defines fluidic ports 48A,48B suitable to permit fluid (e.g., liquid) containing a target species42 to be introduced into the microfluidic channel 52. As shown in FIG.15, functionalization material 38 is arranged over the SAM 36 and theinterface layer 34, and the target species 42 is bound to thefunctionalization material 38, such as may occur after fluid containingthe target species 42 is flowed into the microfluidic channel 52 tocontact the functionalization material 38.

FIG. 16 is a top plan view photograph of a bulk acoustic wave MEMSresonator device 10 (consistent with the portion of a device 10illustrated in FIG. 1) suitable for receiving an optional hermeticitylayer, an interface layer, a self-assembled monolayer, andfunctionalization (e.g., specific binding) material as disclosed herein.The MEMS resonator device 10 includes a piezoelectric material (notshown) arranged over a substrate 12, a bottom side electrode 20 arrangedunder a portion of the piezoelectric material, and a top side electrode28 arranged over a portion of the piezoelectric material, including anactive region 30 in which the piezoelectric material is betweenoverlapping portions of the top side electrode 28 and the bottom sideelectrode 20. Externally accessible contacts 20A, 28A are in electricalcommunication with the bottom side electrode 20 and the top sideelectrode 28, respectively. After portions of the MEMS resonator device10 is overlaid with an interface layer, a self-assembled monolayer, andfunctionalization (e.g., specific binding) material as disclosed herein,the device 10 may be used as a sensor and/or incorporated into amicrofluidic device. If desired, multiple MEMS resonator devices 10 maybe provided in an array on a single substrate 12.

FIG. 17 is a perspective assembly view of a microfluidic device 60incorporating a substrate 62 with multiple bulk acoustic wave MEMSresonator devices, an intermediate layer 80 defining a centralmicrofluidic channel 82 registered with active regions 68A-68N of theMEMS resonator devices, and a cover or cap layer 90 arranged to coverthe intermediate layer 80. Top central portions of the substrate 62,which includes an acoustic reflector (not shown) and a piezoelectricmaterial (not shown), include a top side electrode 66 and bottom sideelectrodes 64A-64N. Regions in which the foregoing electrodes overlapone another and sandwich the piezoelectric material embody activeregions 68A-68N. Any suitable number of active regions 68A-68N may beprovided and fluidically arranged in series or parallel, although fiveactive regions are illustrated in FIG. 17. Top peripheral (or top end)portions of the substrate 62 further include reference top sideelectrodes 76 and reference bottom side electrodes 74 in communicationwith reference overlap regions 70. Such reference overlap regions 70 arenot exposed to fluid, and are present to provide a basis for comparingsignals obtained from the active regions 68A-68N exposed to fluid withinthe central microfluidic channel 82. The substrate 62 is overlaid withthe intermediate (e.g., wall-defining) layer 80, wherein the centralmicrofluidic channel 82 is intended to receive fluid, and definesperipheral chambers 84 arranged to overlie the reference overlap regions70 in a sealed fashion. The intermediate layer 80 may be formed of anysuitable material such as SU-8 negative epoxy resist, other photoresistmaterial, or laser-cut “stencil” layers of thin polymeric materialsoptionally including one or more self-adhesive surfaces (e.g., adhesivetape), etc. The intermediate layer 80 further includes a lateral insetregion 86 that enables lateral portions of the top side electrode 66 andbottom side electrodes 64A-64N to be accessed upon assembly of themicrofluidic device 60. The cover or cap layer 90 includes a lateralinset region 96 registered with the lateral inset region 86 of theintermediate layer 80, and includes microfluidic ports 92, 94 accessiblealong a top surface 98 and registered with end portions of the centralmicrofluidic channel 82 defined in the intermediate layer 80 to permitfluid (e.g., liquid) to be supplied to the central microfluidic channel82 over the active regions 68A-68N. Preferably, at least the electrodes64A-64N, 66 are overlaid with a hermeticity layer, an interface layer, aself-assembled monolayer, and functionalization (e.g., specific binding)material as disclosed herein. Microfluidic devices according to otherconfigurations may be provided, as will be recognized by those skilledin the art upon review of the present disclosure.

FIG. 18 is a schematic cross-sectional view of a film bulk acoustic waveresonator (FBAR) structure 100 including an active region, with at leastportions of the FBAR structure 100 subject to being overlaid with aninterface layer and a self-assembled monolayer (SAM) suitable forreceiving a functionalization material (e.g., specific binding ornon-specific binding material), according to one embodiment. The FBARstructure 100 includes a substrate 102 (e.g., silicon or anothersemiconductor material) defining a cavity 106 that is covered by asupport layer 108 (e.g., silicon dioxide). A bottom side electrode 110is arranged over a portion of the support layer 108, a piezoelectricmaterial layer 112, preferably embodying inclined c-axis hexagonalcrystal structure piezoelectric material (e.g., AlN or ZnO), is arrangedover the bottom side electrode 110 and the support layer 108, and a topside electrode 116 is arranged over at least a portion of a top surface114 of the piezoelectric material layer 112. A portion of thepiezoelectric material layer 112 arranged between the top side electrode116 and the bottom side electrode 110 embodies an active region 120 ofthe FBAR structure 100. The active region 120 is arranged over andregistered with the cavity 106 disposed below the support layer 108. Thecavity 106 serves to confine acoustic waves induced in the active region120 by preventing dissipation of acoustic energy into the substrate 102,since acoustic waves do not efficiently propagate across the cavity 106.In this respect, the cavity 106 provides an alternative to the acousticreflector 14 illustrated in FIGS. 1 and 3-15. Although the cavity 106shown in FIG. 18 is bounded from below by a thinned portion of thesubstrate 102, in alternative embodiments at least a portion of thecavity 106 may extend through an entire thickness of the substrate 102.Steps for forming the FBAR structure 100 may include defining the cavity106 in the substrate 102, filling the cavity 106 with a sacrificialmaterial (not shown) optionally followed by planarization of thesacrificial material, depositing the support layer 108 over thesubstrate 102 and the sacrificial material, removing the sacrificialmaterial (e.g., by flowing an etchant through vertical openings definedin the substrate 102 or the support layer 108, or lateral edges of thesubstrate 102), depositing the bottom side electrode 110 over thesupport layer 108, growing (e.g., via sputtering or other appropriatemethods) the piezoelectric material layer 112, and depositing the topside electrode 116.

As will be recognized by one skilled in the art upon review of thepresent disclosure, in certain embodiments the FBAR structure 100 ofFIG. 18 may be substituted for solidly mounted BAW structures disclosedin FIGS. 1 and 3-15, with at least portions of the BAW structures beingoverlaid with an interface layer and a self-assembled monolayer suitablefor receiving a functionalization material (e.g., specific binding ornon-specific binding material).

Those skilled in the art will recognize improvements and modificationsto the preferred embodiments of the present disclosure. All suchimprovements and modifications are considered within the scope of theconcepts disclosed herein and the claims that follow.

What is claimed is:
 1. A micro-electrical-mechanical system (MEMS)resonator device comprising: a substrate; a bulk acoustic wave resonatorstructure arranged over at least a portion of the substrate, the bulkacoustic wave resonator structure including a piezoelectric material, atop side electrode arranged over a portion of the piezoelectricmaterial, and a bottom side electrode arranged between the piezoelectricmaterial and the substrate, wherein a portion of the piezoelectricmaterial is between the top side electrode and the bottom side electrodeto form an active region; an interface layer arranged over at least aportion of the active region, wherein less than an entirety of thepiezoelectric material is overlaid with interface layer material that isavailable to receive a self-assembled monolayer (SAM); and theself-assembled monolayer arranged over at least a portion of theinterface layer.
 2. The MEMS resonator device of claim 1, wherein theinterface layer comprises a hydroxylated oxide surface, and theself-assembled monolayer comprises an organosilane material.
 3. The MEMSresonator device of claim 1, wherein the interface layer comprises goldor another noble metal, and the self-assembled monolayer comprises athiol material.
 4. The MEMS resonator device of claim 1, wherein theinterface layer is arranged over less than an entirety of thepiezoelectric material.
 5. The MEMS resonator device of claim 1, furthercomprising a patterned blocking layer arranged over at least one portionof the interface layer.
 6. The MEMS resonator device of claim 5, whereinthe patterned blocking layer comprises at least one of silicon nitride,silicon carbide, photoresist, SU-8, polyimide, parylene, or poly(ethylene glycol).
 7. The MEMS resonator device of claim 1, furthercomprising at least one functionalization material arranged over atleast a portion of the self-assembled monolayer, wherein at least aportion of the at least one functionalization material is registeredwith the active region.
 8. The MEMS resonator device of claim 1, whereinthe top side electrode comprises a non-noble metal, and the MEMSresonator device further comprises a hermeticity layer arranged betweenthe interface layer and the top side electrode.
 9. The MEMS resonatordevice of claim 8, wherein the hermeticity layer comprises an oxide, anitride, or an oxynitride dielectric material, and the hermeticity layercomprises a water vapor transmission rate of no greater than 0.1(g/m²/day).
 10. The MEMS resonator device of claim 1, wherein thepiezoelectric material comprises a hexagonal crystal structurepiezoelectric material that comprises a c-axis having an orientationdistribution that is predominantly non-parallel to normal of a face ofthe substrate.
 11. A sensor comprising the MEMS resonator device ofclaim
 1. 12. A fluidic device comprising the MEMS resonator device ofclaim 7, and a fluidic passage arranged to conduct a liquid to contactthe at least one functionalization material.
 13. A method for biologicalor chemical sensing, the method comprising: supplying a fluid containinga target species into the fluidic passage of a fluidic device accordingto claim 12, wherein said supplying is configured to cause at least someof the target species to bind to the at least one functionalizationmaterial; inducing a bulk acoustic wave in the active region; andsensing a change in at least one of a frequency property, a magnitudeproperty, or a phase property of the bulk acoustic wave resonatorstructure to indicate at least one of presence or quantity of targetspecies bound to the at least one functionalization material.
 14. Amicro-electrical-mechanical system (MEMS) resonator device comprising: asubstrate; a bulk acoustic wave resonator structure arranged over atleast a portion of the substrate, the bulk acoustic wave resonatorstructure including a piezoelectric material, a top side electrodearranged over a portion of the piezoelectric material, and a bottom sideelectrode arranged between the piezoelectric material and the substrate,wherein a portion of the piezoelectric material is arranged between thetop side electrode and the bottom side electrode to form an activeregion; a self-assembled monolayer arranged over at least a portion ofthe active region; and at least one functionalization material arrangedover at least a portion of the self-assembled monolayer, wherein lessthan an entirety of the piezoelectric material is overlaid with the atleast one functionalization material.
 15. A method for fabricating amicro-electrical-mechanical system (MEMS) resonator device, the methodcomprising: forming a bulk acoustic wave resonator structure including apiezoelectric material, a top side electrode arranged over a portion ofthe piezoelectric material, and a bottom side electrode arranged betweenthe piezoelectric material and a substrate, wherein a portion of thepiezoelectric material is arranged between the top side electrode andthe bottom side electrode to form an active region; depositing aninterface layer over at least a portion of the active region, whereinless than an entirety of the piezoelectric material is overlaid withinterface layer material that is available to receive a self-assembledmonolayer (SAM); and forming a self-assembled monolayer over at least aportion of the interface layer, wherein at least a portion of theself-assembled monolayer is arranged over the active region.
 16. Themethod of claim 15, further comprising applying a patterned mask over atleast a portion of the bulk acoustic wave resonator structure prior tothe depositing of the interface layer.
 17. The method of claim 15,further comprising depositing at least one functionalization materialover at least a portion of the self-assembled monolayer, wherein the atleast one functionalization material is registered with at least aportion of the active region.
 18. The method of claim 15, wherein thetop side electrode comprises a non-noble metal, and the method furthercomprises depositing a hermeticity layer between at least portions ofthe interface layer and the top side electrode, wherein the hermeticitylayer comprises an oxide, a nitride, or an oxynitride dielectricmaterial, and wherein the hermeticity layer comprises a water vaportransmission rate of no greater than 0.1 (g×mm)/(m²×day).
 19. The methodof claim 15, further comprising depositing a patterned blocking layerover at least one portion of the interface layer.
 20. The method ofclaim 15, further comprising forming at least one wall over a portion ofthe bulk acoustic wave resonator structure and defining a fluidicpassage containing the active region.